Design and Implementation of a Message-Based Flight Software Framework for CubeSat-Class Spacecraft

Abstract

CubeSats have expanded the possibilities for developing space missions, while introducing important challenges for the software responsible for their operation. Flight software must coordinate multiple tasks, manage communication between subsystems, and detect potential faults in a timely manner, while operating under constraints on processing power and available resources. Developing these capabilities independently for each mission increases software complexity and development effort, motivating the use of reusable software solutions. This thesis presents the design, implementation, and evaluation of a modular and reusable flight software framework intended to provide a common foundation for embedded CubeSat applications. Its design adopts selected principles from established spacecraft software architectures, adapted to the needs of small satellite missions. The framework is implemented in C using FreeRTOS on an STM32 microcontroller. The framework incorporates a Software Bus based on the publish/subscribe model and is inspired by NASA’s industry framework “coreFS”. It includes services for task management, startup synchronization and task health monitoring linked to watchdog supervision. It also separates reusable framework services from mission-specific applications. Evaluation is performed through integration into the RSLabSat CubeSat development environment, using representative applications for spacecraft mode management, telemetry and telecommand handling, and subsystem control. Through detailed functional tests, key communication, synchronization, monitoring, and fault-handling mechanisms were assessed. The results indicate that combining reusable software services can provide a practical foundation for CubeSat flight software development. However, further implementation work and more extensive verification are required before the framework can be considered for use in an operational space mission.